CHAPTER 2: Life’s Chemical Basis Dmitri Mendeleev BIOL 160: General Biology
Definition Worksheet #2: Chapter 2 Define the following key terms. 1. Atom: Particles that are the building blocks of all substances. 2. Proton Subatomic particle that carries a positive charge. 3. Neutron Subatomic particle that carries no charge. 4. Electron Subatomic particle that carries a negative charge. 5. Atomic Number Number of protons which determines the element. 6. Atomic Mass 7. Isotope Formsof an element that differ in the number of neutron their atoms carry. 8. Ion: An atom with different numbers of electrons and protons. 9. Cation Positive ion 10. Anion Negative ion 11. Molecule Forms when two or more atoms of the same or elements join in chemical bonds 12. Chemical Bond An attractive force thta arises between two atoms when their electrons interacts. 13. Ionic Bond Two atoms with a large difference in electronegativity may stay together. 14. Electronegativity A measure of an atoms ablitity to pull electrons from other atoms. 15. Polar Covalent Bond Atoms do not share electrons equally. 16. Non-polar Covale nt Bond Atoms participating in the bonds are sharing electrons equally 17. Hydrogen Bond A weak attraction between a highly electronegative atom and hydrogen atom taking part in a seperate polar covelant bond
18. Solution A mixture of solutes 19. Solute Dissolved substances 20. Solvent Substance that can dissolve other substances 21. Acid Donate hydrogen ions as they dissolve in water. 22. Base Accept hydrogen ions. 23. Buffer Set of chemicals often a weak acid or base and it's salts that can keep the PH of solution stable. 24. Salt Substance that release ions other than H+ or OH when dissolved in water.
CHAPTER 2: Basic Introduction to Chemistry Characteristics of atoms
Subatomic particle
Charge
Location
Mass
Recent discoveries have increased the number of naturally occurring elements from 92 to 94.
Since subatomic particles may be charged, they may attract or repel other subatomic particles. Please complete the below table, indicating how the below pairings of subatomic particles would behave (attract, neutral, repulsion).
Subatomic particle
Proton
Neutron
Electron
Proton
repulsion
Neutral
Attractions
Neutron
Neautral
neutral
Neautral
Electron
attraction
Neautral
Repulsion
What is an element? The pure substances each consisting only of atoms with the same number of protons.
Atomic Number= # of protons
1. Periodic Table The periodic table of elements has elements placed in a repeating pattern based on their chemical properties and how they react with other
Atomic Mass=
mass of protons + neutrons
elements. (Appendix 4 in the back of the book shows a periodic table.)
Principle
Definition
C
N
O
P
Fl
Na
Atomic Number
6
7
8
15
9
11
Atomic Mass
12.01
14.01
16.00
30.97
19.00
11
# of electrons
6
7
8
15
9
11
# of protons
6
7
8
15
9
11
2. What makes Carbon different than Hydrogen?
3. What is an isotope? Forms of an element that differ in the number of neautrons their atoms carry.
A. The element carbon has 3 main different isotopes: 12C has a mass of 12, due to 6 protonsand 6 neutrons 13C has a mass of 13, due to 6 protons and 7 neutrons 14C has a mass of 14, due to 6 protons and 8 neutrons
B. Some isotopes have an unstable nucleus and may release energy or some of the subatomic particles (protons or neutrons) to become more stable. These isotopes are called RADIOISOTOPES. Some are used in medicine to “label” specific molecules or to follow a specific molecule as it is distributed throughout the body. In this case it is commonly called a TRACER _. They may also release enough energy to kill cells and stop the activity of abnormal (cancer) cells, or the energy released may be used to drive an artificial pacemaker (helps the heart maintain a regular rhythm). 5. It is most important to know what the subatomic particles are, where they are located in an atom, and that atoms of different elements differ because they contain different numbers of protons. The number behind each elemental name represents the atomic mass for that atom. Complete the following table.
Element
Symbol
Atomic Number
Atomic Mass
Number of Protons
Number of Neutrons
Number of Electrons
Nitrogen-14
_N
7
14
_7
7_
7_
Chlorine-35
_ Cl
_ 17
35
17
_ 17
18_
Oxygen-16
_ O
_8
16_
8_
8_
8
Sodium-23
Na
_ 11
22.99_
11
11_
_12
Sulfur-35
S
_ 16
35
16
19_
_19
Oxygen-17
_O
8
16_
8_
9_
9_
6. Complete the following matching activity.
A.
Radioisotope used to reveal the pathway or destination of a substance
B.
Subatomic particles with a negative charge
C.
Positively charged subatomic particles within the nucleus
D.
Subatomic particles within the nucleus carrying no charge
E.
Atoms of a given element that differ in the number of neutrons
F.
The number of protons in an atom
G.
Form of an element that emits radiation
H.
The number of protons and neutrons in the nucleus of one atom
I.
Pure substances, each consisting only of atoms with the same number of protons
J.
Smallest units of an element that retain the properties of a given element. Particles that are the building blocks of all substances.
1. atoms J 2. protonsC 3. neutrons D 4. electronsB 5. atomic number F 6. atomic massH 7. elements I 8. isotopeE 9. radioisotopes G 10. tracer A
7. Chemical Bonds Which subatomic particle participates in bonding between atoms? MOLECULES How do you figure out how many electrons there are in an atom?
B. Each horizontal row on the periodic table represents an energy level around the nucleus of an atom. 1.The first level is closest to the nucleus and can hold only _2 electrons due to its small volume and the fact that electrons repel each other. Electrons in this level have the lowest amount of energy. Notice that the top row on the periodic table has only two elements (H and He) and the atomic number of Helium is 2 which means it has 2 protons and 2 electrons. 2. The second level is farther away from the nucleus, so is larger in volume and can hold a maximum of 10 electrons. Notice that the second row on the periodic table has a total of eight elements and the atomic number for Neon the last element on the row is 10; which means a neutral Neon atom has 10 protons and 10 electrons (two of the electrons are on the first energy level and the remaining 8 electrons on the second level). 3. The third level is still farther away from the nucleus, so is able to hold more electrons than the second level, and the fourth level more than the third, etc. The problem is that not all of these additional electrons are located on the outermost energy level. C. The atomic number on the periodic table equals thetotal number of protons inside the nucleus and therefore the total number of electrons found moving around the nucleus in an atom; however it is only those electrons on the outer energy level that are taken, shared or given away when atoms interact with other atoms. The maximum number of electrons that can exist on the outer energy level of any atom is ALWAYS eight (except for H and He where the maximum number is two). Try to remember that “eight is great”. For the purposes of this class and to best prepare you for Anatomy and Physiology, it is necessary to “simplify” chemistry and the periodic table. It will be easier to understand how atoms behave if you pretend that the center (and bottom) of the periodic table don’t exist. Those elements in the middle of the periodic table have additional electrons that are NOT placed in the outer most energy level, therefore they do NOT influence how an atom of that element behaves.
If this is the case, then all of the horizontal rows on the table will have eight columns, except the first horizontal row which will have only two columns. D. Where the elements are found on the periodic table will help determine how an atom will interact with other atoms (“take”, “share” or “give away” some of their electrons). The vertical column of the periodic table indicates the number of electrons an atom of that element has in the outermost energy level. As mentioned, it is only these outermost electrons that will influence how an atom interacts with other atoms as they form molecules. E. Those elements in the last column on the periodic table (farthest to the right, or in column #8) are the most “stable” of all the elements, having just the right number of electrons to “fill” the outer energy level. These elements are very stable and normally do not react chemically with the other elements to form molecules. (Called the Inert Gases) F. All the other elements on the periodic table “wish” they could have the same number of electrons as one of those in column #8 (farthest to the right) so they too can become very stable. They do this by taking, giving or sharing electrons to fill their outer electron shell. The ability of an atom to “pull or take” electrons from another atom to become more stable is called ELECTRONEGATIVITY. 1. Those elements on the right side of the periodic table are so close to the last column, they tend to have high electronegativity values and tend to “TAKE” electrons from other elements until they have a total of 8 in their outer energy level or in some cases they may be forced to share electrons with other atoms. Using the periodic table as a guide, how many more electrons do atoms of the following elements need to take or share to reach a total of those in the last column? P = 3 , Cl = 2, O = 2, N = 3, S = 2, C = 4, Br = 6
2. Those elements on the left side of the periodic table are far away from the last column, they tend to have very low electronegativity values and do NOT “pull or take” electrons from other atoms, in fact they tend to “GIVE AWAY” their electrons that are on the outer energy level to other atoms. In a sense they go backwards on the table until they reach the last column but on the row above where they started. Using the periodic table as a guide, how many electrons do atoms of the following elements need to give away or lose to revert back to the end of the previous level on the periodic table? Na = 1, Al = 3, Ca = 2, K = 2, C = 4, Mg = 2,
G. Neutral atoms that “take” or “give away” electrons no longer remain neutral; they become either negatively or positively charged particles called ions . There are two main types: 1. ANIONS are those that have a negative charge because the neutral atom has “taken” electrons from other atoms so they now have more electrons than protons. 2. CATIONS are those that have a positive charge because the neutral atom has “given away” electrons to other atoms so they now have fewer electrons than protons. 8. When atoms “give away”,” take” or “share” electrons with other atoms they form a CHEMICAL bond (a force between two atoms that holds them together). A. molecules_are two or more atoms that have joined together to form a group. Some only contain one type of element: H2, O2, N2, F2, Cl2, Br2 & I2, but the majority contain two or more different types of elements. When a molecule contains two or more different elements combined in a fixed ratio (proportion) that never varies it is called a compund . Examples include: water (H2O), Carbon dioxide (CO2), Hydrochloric acid (HCl), and Glucose (C6H12O6). The numbers in the chemical formulas indicate the number of atoms of each type in the molecule. B. mixtures_ contain two or more substances (elements or compounds) that are combined together in a ratio (proportion) that varies. They can either be concentrated or dilute (as in strong or weak coffee). These forms of matter will be studied in much more detail in future modules. 9. There are several important chemical bonds seen in biological molecules. A.IONIC BONDS: oppositely charged ions held close by attraction, electrons transferred (one loses, one gains) between atoms
Element Location
Giver? Taker?
What type of ion formed?
Positive or negatively charged ion?
Left side of per table
Giver
Cation
Positive
Right side of per. table
Taker
Anion
Negative
1. Chemical formulas represent the type and number of atoms present in the compound. The number of atoms needed to keep the molecule neutral is dependent on the ion charges. Elements that “give away” one electron form +1 ions, those that “give away” 2 electrons form +2 ions, etc. Elements that “take” one electron form -1 ions, those that “take” 2 electrons form -2 ions, etc. Some examples of chemical formulas for ionic compounds include: Sodium chloride: NaCl This compound contains Na+1 and Cl-1 ions in a 1:1 ratio since their ion charges are the same value (+1 / -1) and they cancel each other out when forming a neutral atom. Magnesium nitride: Mg3N2 This compound contains Mg+2 and N-3 ions in a 3:2 ratio since their ion charges do not directly cancel each other out; three Mg+2 ions are needed to make a total of +6 charge, which is cancelled out by two N-3 ions that make a total of -6 charge forming a neutral molecule. B. COVALENT BONDS: 1. What is a covalent bond? When two atoms share a pair of electrons 2. Atoms with (similar, differing) electronegativities form covalent bonds.
Covalent Bond
# of electrons shared?
Example
Structural Formula
Strength
Single
2
Strong
Double
4
Stronger
Triple
6
Stronger yet!
Between two identical atoms
2
H2
NONPOLAR Covalent Bond
Between two different atoms
4
H2O
POLAR Covalent Bond
POLAR COVALENT BOND
More electrons in Oxygen, so that part of the molecule is more negatively charged; fewer electrons near Hydrogens, so that part of the molecule is less negatively charged
3. Covalent bonds are the strongest type of all chemical bonds. They are very difficult to break, and hold atoms together to form molecules. These bonds are also called INTRAMOLECULAR forces, because they exist within the molecule. 4. Chemical formulas of compounds that have covalent bonds are determined much the same way that ionic compounds are determined; however both atoms want to “take” electrons from each other. The number of atoms needed to keep the molecule neutral is dependent on the number of electrons they need to be like elements in column #8 on the periodic table. Some examples of chemical formulas for covalent compounds include:
Water (H2O)
# of e-s in outer shell
What combo would form an outer shell with 8 e-s?
Draw molecule
Hydrogen
1
Oxygen
6
Carbon Dioxide (CO2)
# of e-s in outer shell
What combo would form an outer shell with 8 e-s?
Draw molecule
Carbon
4
Oxygen
6
C. HYDROGEN BONDS: 1. What is a hydrogen bond? A weak attraction between a highly electronegative atom and a hydrogen atom taking part in a seperate polar covalent bond. 2. Are hydrogen bonds weak or strong attractions?
Weak
7. Water’s Life-Giving Properties This illustration shows how hydrogen bonds collectively stabilize water molecules. How does this affect the unique physical properties of water?
a. Water is a molecule held together with POLAR COVALENT BONDS. Draw a picture of a water molecule, and explain how the oxygen and hydrogens participate in this type of bond.
b. Which part of a water molecule is slightly negative? The oxygen atom
c. Which is partially positive? The hydrogen atom
d. How does this affect interaction with other nearby molecules of water? Or other types of molecules? The polarity of water molecules attracts other water molecules.
e.Why does water have such a high surface tension? because of water cohesion
f. What is a solvent? it is a substance, usually a liquid, that can dissolve other substances
g. Why is water such a good solvent?
Positive ions attract the negative part of part of water (the oxygen atom), while negative ions attract the positive part of water (the Hydrogenatoms). h. Water’s Temperature-Stabilizing Effects: What is temperature? Is a way to measure the energy of molecules nonstop vibration
Why is it hard to change the temperature of water? i. Water’s Cohesion: What is cohesion? means molecules that resist seperating from one another
How does the cohesion of water molecules help transport water up inside of the tissues of plants? Cohesion makes it possible for columns of liquid water to rise from the roots to the leaves inside narrow pipelines of vascular tissues.
11. Dissolved ions inside of our bodies influence its structure and function. One of the body’s most chemically active ion is the hydrogen ion (H+1). A.Acids are substances that release or donate hydrogen ions (H+1) to a water (aqueous) solution. Remember that a hydrogen ion is the same thing as a proton since it is a hydrogen atom that has lost its electron. 1. Strong acids ionize completely releasing their hydrogen ions easily. One example is Hydrochloric acid (HCl) found in the stomach. 2. Weak acids may have hydrogen ions to release to solution, but are reluctant or resistant to do so. One example is Carbonic acid (H2CO3) found in soft drinks that is formed when carbon dioxide reacts with water. B. Basesare substances that accept or bond with hydrogen ions when dissolved in water solutions, thereby removing them or decreasing the number of hydrogen ions remaining in solution. They may also release hydroxide ions (OH-1) to a solution that will then combine with hydrogen ions to form water. These solutions are also known as alkaline solutions. This is how Alka Seltzer got its name. It reduces the acidity of the stomach when someone has acid indigestion. C. The PHSCALE is used by scientists to represent the nature of a solution relative to the amount of hydrogen ions in solution. The scale extends from a numerical value of 0to 14 . 1. Solutions with a value of “0” are very Acidic_, meaning there is a high concentration of hydrogen ions in solution. 2. Solutions with a value of “14” are very Basic (alkaline), meaning there is a very low concentration of hydrogen ions in solution. 3. Pure water has a value of “ 7”, which indicates it is a neutral solution, or in other words one with the same amount of H+1 and OH-1 ions. 4. The pH scale is a type of metric scale. This means that for every change in the pH, there is a ten-fold change in the concentration of hydrogen ions. On the metric scale, to change from one unit of measurement to another it is necessary to move the decimal point either to the right or to the left. Each time the decimal point is moved it is equal to multiplying or dividing by 10. If the decimal moves 3 places to the right it is equal to multiplying the value by 10 X 10 X 10 or the final answer is 1,000 times larger. The following are several examples: A solution with a pH = 2 is 10 times more acidic than a solution of pH = 3. A solution with a pH = 5 is 100 times less acidic than a solution of pH = 3. A solution with a pH = 10 is 100 times more basic than a solution of pH = 8. A solution with a pH = 6 is 1000 times less basic than a solution of pH = 9. D. _ are substances that when dissolved in water release ions other than the hydrogen ion (H+1) or hydroxide ion (OH-1). Examples include sodium chloride or table salt (NaCl) and calcium phosphate [ Ca3(PO4)2 ] found in bones. Most salts serve key functions in cells. The ions released into solution in the body are also called “electrolytes”, in that they allow the solution to be able to conduct an electric current. E. _ are substances that resist a change in pH when an acid or base is added to the solution. They are generally formed by mixing a weak acid and weak base. If a strong acid is added to the mixture, the weak base bonds to the hydrogen ions to neutralize the acid; if a strong base is added to the mixture, the weak acid releases hydrogen ions to neutralize the base. In either case, the pH does not change significantly. Buffers can only work for so long, then the pH will shift rapidly.
12. Give the approximate pH of each of the following solutions then identify each as an acid (A) [pH of 1-6], base (B) [ph of 8-14] or essentially neutral (N) [pH of 6-8].
1. Tomato juice _ 4, A 2. Human blood _ 8, N 3. Vinegar _ 2, A 4. Pure water _ 7, N 5. Coffee _ 5, A 6. Ammonia _ 11, B 7. Seawater _ 8, N 8. Typical rainwater _ 5, A 9. Oven / Drain cleaner _ 14, B 10. Antacid pills (Tums) _ 9, B 11. Urine _ 5, A 12. Gastric juice _ 1, A
13. Complete the following matching
1. acid stomach N
A.
A sometimes irreversible state of unconsciousness
2. acids K
B.
CO2 builds up in the blood, too much H2CO3 forms, and blood pH severely decreases
3. pH scale F
C.
Hydroxide ion
4. chemical burns J
D.
Substances that accept H+ when dissolved in water
5. H+ H
E.
An uncorrected increase in blood pH
6. bases I
F.
Used to measure H+ concentration in various fluids
7. examples of basic solutions D
G.
A partnership between a weak acid and the base that forms when it dissolves in water; counters slight pH shifts
8. coma A
H.
Hydrogen ion or proton
9. Respiratoryacidosis B
I.
Baking soda, seawater, egg white
10. OH– C
J.
Can be caused by ammonia, drain cleaner, and sulfuric acid in car batteries
11. tetany E
K.
Substances that donate H+ when dissolved in water
12. examples of acid solutions L
L.
Lemon juice, gastric fluid, coffee
13. alkolosis M
M.
A potentially lethal pH stage in which the body’s skeletal muscles enter a state of uncontrollable contraction
14. buffer system G
N.
Can be caused by eating too much fried chicken or certain other foods
Chapter review: Answer the following essay questions.
14. a. If a sulfur atom has six electrons in its outer shell of electrons, how many covalent bonds is it likely to form with other atoms? Why? Two because there are two unpaired electrons.
b. If a hydrogen atom has one electron in its outer shellof electrons, how many covalent bonds is it likely to form with other atoms? Why?
Only one because only one electron is available for pairing.
c. What do you think the chemical formula for hydrogen sulfide would be? Hint: Look at the location of sulfur compared to oxygen on the periodic table. H2S because the chemical formula for hydrogen is "H2" and the formula for sulfide is "S."
15. In your own words, explain the main difference between a polar covalent bond and a nonpolar covalent bond.
In nonpolar covalent bonds the atoms have the same electronegativity. This means the atoms equally share electrons. In polar covalent bonds, one atom has more pull than the other.
16. If a water molecule is neutral (has no net charge), then why does it attract polar molecules and repel nonpolar ones.
In each molecule of water, polar covalent bonds join one oxygen atom with two hydrogen atoms. Overall, the molecule has no charge, but the oxygen pulls the shared electrons a bit more than the hydrogen atoms do. Thus, each of the atoms in a water molecule carries a slight charge: The oxygen atom is slightly negative and the hydrogen atoms are slightly positive. This separation of charge means a water molecule is polar.
17. Explain why sweating helps cool the body when it is overheated?
It takes heat to convert liquid water to a gas, so the surface temperature of water decreases during evaporation. Evaporative water loss can help you and some other mammals cool off when you sweat in hot, dry weather. Sweat, which is about 99% water, cools the skin as it evaporates.
Sample Test Questions for chapter 2 and Lab #6: 1. A substance that cannot be broken down into simpler substances by ordinary chemical means is known as a(n) C a. molecule b. ion c. element d. compound e. isotope
2. A sulfur atom has 6 electrons in its outer energy shell. As a result, it tends to form covalent bonds with other atoms.A a. 2 b. 3 c. 4 d. 6 e. 8
3. A phosphorus atom has an atomic mass (mass number) of 31 and an atomic number of 15. How many PROTONS are there in a neutral phosphorus atom? A a. 15 b. 16 c. 31 d. 46 e. none of the above 4. A is a subatomic particle that carries acharge. B a. proton……negative b. electron…..negative c. neutron…..negative d. proton…..neutral e. electron……neutral
5. Isotopes of an element differ in their number of: D a. electrons b. bonds formed by the atom c. protons d. neutrons e. nuclei
6. When hydrogen atoms lose one electon to become an ion, their net electrical charge is A a. +1 b. -1 c. remains neutral d. impossible to know from just this information provided BIOL 160: Module 1 - 28 -
7. A solution at pH of 4 contains the concentration of Hydrogen ions A as the same amount of a solution with a pH of 2. a. 2 times more b. 2 times less c. 20 times more d. 20 times less e. 100 times less
8. This property of water makes it possible for columns of liquid water to rise from roots to leaves inside narrow pipelines of vascular tissues inside a plant. A a. cohesion b. temperature c. water sickness d. surface tension e. none of the above
9. Bonds that form when atoms transfer one or more electrons are called bonds.A a. ionic b. polar covalent c. hydrogen d. non-polar covalent
10. Within water molecules, the hydrogen atoms are bonded to the oxygen atom by bonds, whereas the hydrogen atoms form ___ bonds with neighboring water molecules. a. hydrogen…..ionic b. ionic……hydrogen c. polar covalent…….ionic d. polar covalent……hydrogen e. hydrogen…….polar covalent
11. A solvent is E a. the dissolving agent of a solution b. generally the liquid portion of a solution c. usually water in living organisms d. generally the portion of a solution found in smaller amount e. A, B and C are all correct
12. If a sample has a mass of 0.08 grams, what is this mass measured in milligrams? a. 0.00008 b. 0.008 c. 0.08 d. 8.0 e. 80
Dmitri Mendeleev
BIOL 160: General Biology
Definition Worksheet #2: Chapter 2 Define the following key terms.
1. Atom: Particles that are the building blocks of all substances.
2. Proton Subatomic particle that carries a positive charge.
3. Neutron Subatomic particle that carries no charge.
4. Electron Subatomic particle that carries a negative charge.
5. Atomic Number Number of protons which determines the element.
6. Atomic Mass
7. Isotope Formsof an element that differ in the number of neutron their atoms carry.
8. Ion: An atom with different numbers of electrons and protons.
9. Cation Positive ion
10. Anion Negative ion
11. Molecule Forms when two or more atoms of the same or elements join in chemical bonds
12. Chemical Bond An attractive force thta arises between two atoms when their electrons interacts.
13. Ionic Bond Two atoms with a large difference in electronegativity may stay together.
14. Electronegativity A measure of an atoms ablitity to pull electrons from other atoms.
15. Polar Covalent Bond Atoms do not share electrons equally.
16. Non-polar Covale nt Bond Atoms participating in the bonds are sharing electrons equally
17. Hydrogen Bond A weak attraction between a highly electronegative atom and hydrogen atom taking part in a seperate polar covelant bond
18. Solution A mixture of solutes
19. Solute Dissolved substances
20. Solvent Substance that can dissolve other substances
21. Acid Donate hydrogen ions as they dissolve in water.
22. Base Accept hydrogen ions.
23. Buffer Set of chemicals often a weak acid or base and it's salts that can keep the PH of solution stable.
24. Salt Substance that release ions other than H+ or OH when dissolved in water.
CHAPTER 2: Basic Introduction to Chemistry
Characteristics of atoms
Recent discoveries have increased the number of naturally occurring elements from 92 to 94.
Since subatomic particles may be charged, they may attract or repel other subatomic particles. Please complete the below table, indicating how the below pairings of subatomic particles would behave (attract, neutral, repulsion).
What is an element? The pure substances each consisting only of atoms with the same number of protons.
1. Periodic Table
The periodic table of elements has elements placed in a repeating pattern
based on their chemical properties and how they react with other
mass of protons + neutrons
2. What makes Carbon different than Hydrogen?
3. What is an isotope? Forms of an element that differ in the number of neautrons their atoms carry.
A. The element carbon has 3 main different isotopes:
12C has a mass of 12, due to 6 protons and 6 neutrons
13C has a mass of 13, due to 6 protons and 7 neutrons
14C has a mass of 14, due to 6 protons and 8 neutrons
B. Some isotopes have an unstable nucleus and may release energy or some of the subatomic particles (protons or neutrons) to become more stable. These isotopes
are called RADIOISOTOPES. Some are used in medicine to “label” specific molecules or to follow a specific molecule as it is distributed throughout the body. In this case it is commonly called a TRACER _. They may also release enough energy to kill cells and stop the activity of abnormal (cancer) cells, or the energy released may be used to drive an artificial pacemaker (helps the heart maintain a regular rhythm).
5. It is most important to know what the subatomic particles are, where they are located in an atom, and that atoms of different elements differ because they contain different numbers of protons. The number behind each elemental name represents the atomic mass for that atom. Complete the following table.
6. Complete the following matching activity.
1. atoms J
2. protons C
3. neutrons D
4. electrons B
5. atomic number F
6. atomic mass H
7. elements I
8. isotope E
9. radioisotopes G
10. tracer A
7. Chemical Bonds
Which subatomic particle participates in bonding between atoms? MOLECULES
How do you figure out how many electrons there are in an atom?
B. Each horizontal row on the periodic table represents an energy level around the nucleus of an atom.
1.The first level is closest to the nucleus and can hold only _2 electrons due
to its small volume and the fact that electrons repel each other. Electrons in this level have the lowest amount of energy. Notice that the top row on the periodic table has only two elements (H and He) and the atomic number of Helium is 2 which means it has 2 protons and 2 electrons.
2. The second level is farther away from the nucleus, so is larger in volume and can hold a maximum of 10 electrons. Notice that the second row on the periodic table has a total of eight elements and the atomic number for Neon the last element on the row is 10; which means a neutral Neon atom has 10 protons and 10 electrons (two of the electrons are on the first energy level and the remaining 8 electrons on the second level).
3. The third level is still farther away from the nucleus, so is able to hold more electrons than the second level, and the fourth level more than the third, etc. The problem is that not all of these additional electrons are located on the outermost energy level.
C. The atomic number on the periodic table equals the total number of protons inside the nucleus and therefore the total number of electrons found moving around the nucleus in an atom; however it is only those electrons on the outer energy level that are taken, shared or given away when atoms interact with other atoms. The maximum number of electrons that can exist on the outer energy level of any atom is ALWAYS eight (except for H and He where the maximum number is two). Try to remember that “eight is great”. For the purposes of this class and to best prepare you for Anatomy and Physiology, it is necessary to “simplify” chemistry and the periodic table. It will be easier to understand how atoms behave if you pretend that the center (and bottom) of the periodic table don’t exist. Those elements in the middle of the periodic table have additional electrons that are NOT placed in the outer most energy level, therefore they do NOT influence how an atom of that element behaves.
If this is the case, then all of the horizontal rows on the table will have eight columns, except the first horizontal row which will have only two columns.
D. Where the elements are found on the periodic table will help determine how an atom will interact with other atoms (“take”, “share” or “give away” some of their electrons). The vertical column of the periodic table indicates the number of electrons an atom of that element has in the outermost energy level. As mentioned, it is only these outermost electrons that will influence how an atom interacts with other atoms as they form molecules.
E. Those elements in the last column on the periodic table (farthest to the right, or in column #8) are the most “stable” of all the elements, having just the right number of electrons to “fill” the outer energy level. These elements are very stable and normally do not react chemically with the other elements to form molecules. (Called the Inert Gases)
F. All the other elements on the periodic table “wish” they could have the same number of electrons as one of those in column #8 (farthest to the right) so they too can become very stable. They do this by taking, giving or sharing electrons to fill their outer electron shell.
The ability of an atom to “pull or take” electrons from another atom to become more stable is called ELECTRONEGATIVITY.
1. Those elements on the right side of the periodic table are so close to the last column, they tend to have high electronegativity values and tend to “TAKE” electrons from other elements until they have a total of 8 in their outer energy level or in some cases they may be forced to share electrons with other atoms. Using the periodic table as a guide, how many more electrons do atoms of the following elements need to take or share to reach a total of those in the last column?
P = 3 , Cl = 2 , O = 2 , N = 3 , S = 2 , C = 4 , Br = 6
2. Those elements on the left side of the periodic table are far away from the last column, they tend to have very low electronegativity values and do NOT “pull or take” electrons from other atoms, in fact they tend to “GIVE AWAY” their electrons that are on the outer energy level to other atoms. In a sense they go backwards on the table until they reach the last column but on the row above where they started. Using the periodic table as a guide, how many electrons do atoms of the following elements need to give away or lose to revert back to the end of the previous level on the periodic table?
Na = 1 , Al = 3 , Ca = 2 , K = 2 , C = 4 , Mg = 2 ,
G. Neutral atoms that “take” or “give away” electrons no longer remain neutral; they
become either negatively or positively charged particles called ions . There are two main types:
1. ANIONS are those that have a negative charge because the neutral atom has “taken” electrons from other atoms so they now have more electrons than protons.
2. CATIONS are those that have a positive charge because the neutral atom has “given away” electrons to other atoms so they now have fewer electrons than protons.
8. When atoms “give away”,” take” or “share” electrons with other atoms they form a
CHEMICAL bond (a force between two atoms that holds them together).
A. molecules_ are two or more atoms that have joined together to form a group. Some only contain one type of element: H2, O2, N2, F2, Cl2, Br2 & I2, but the majority contain two or more different types of elements. When a molecule contains two or more different elements combined in a fixed ratio (proportion) that never varies it is called a compund . Examples include: water (H2O), Carbon dioxide (CO2), Hydrochloric acid (HCl), and Glucose (C6H12O6). The numbers in the chemical formulas indicate the number of atoms of each type in the molecule.
B. mixtures_ contain two or more substances (elements or compounds) that are combined together in a ratio (proportion) that varies. They can either be concentrated or dilute (as in strong or weak coffee). These forms of matter will be studied in much more detail in future modules.
9. There are several important chemical bonds seen in biological molecules.
A.IONIC BONDS: oppositely charged ions held close by attraction, electrons transferred (one loses, one gains) between atoms
1. Chemical formulas represent the type and number of atoms present in the compound. The number of atoms needed to keep the molecule neutral is dependent on the ion charges. Elements that “give away” one electron form +1 ions, those that “give away” 2 electrons form +2 ions, etc. Elements that “take” one electron form -1 ions, those that “take” 2 electrons form -2 ions, etc. Some examples of chemical formulas for ionic compounds include:
Sodium chloride: NaCl This compound contains Na+1 and Cl-1 ions in a 1:1 ratio since their ion charges are the same value (+1 / -1) and they cancel each other out when forming a neutral atom.
Magnesium nitride: Mg3N2 This compound contains Mg+2 and N-3 ions in a 3:2 ratio since their ion charges do not directly cancel each other out; three Mg+2 ions are needed to make a total of +6 charge, which is cancelled out by two N-3 ions that make a total of -6 charge forming a neutral molecule.
B. COVALENT BONDS:
1. What is a covalent bond?
When two atoms share a pair of electrons
2. Atoms with (similar, differing) electronegativities form covalent bonds.
Covalent Bond
More electrons in Oxygen, so that part of the molecule is more negatively charged; fewer electrons near Hydrogens, so that part of the molecule is less negatively charged
3. Covalent bonds are the strongest type of all chemical bonds. They are very difficult to break, and hold atoms together to form molecules. These bonds are also called INTRAMOLECULAR forces, because they exist within the molecule.
4. Chemical formulas of compounds that have covalent bonds are determined much the same way that ionic compounds are determined; however both atoms want to “take” electrons from each other. The number of atoms needed to keep the molecule neutral is dependent on the number of electrons they need to be like elements in column #8 on the periodic table. Some examples of chemical formulas for covalent compounds include:
C. HYDROGEN BONDS:
1. What is a hydrogen bond?
A weak attraction between a highly electronegative atom and a hydrogen atom taking part in a seperate polar covalent bond.
2. Are hydrogen bonds weak or strong attractions?
Weak
7. Water’s Life-Giving Properties
This illustration shows how hydrogen bonds collectively stabilize water molecules. How does this affect the unique physical properties of water?
a. Water is a molecule held together with POLAR COVALENT BONDS. Draw a picture of a water molecule, and explain how the oxygen and hydrogens participate in this type of bond.
b. Which part of a water molecule is slightly negative? The oxygen atom
c. Which is partially positive? The hydrogen atom
d. How does this affect interaction with other nearby molecules of water? Or other types of molecules?
The polarity of water molecules attracts other water molecules.
e.Why does water have such a high surface tension? because of water cohesion
f. What is a solvent? it is a substance, usually a liquid, that can dissolve other substances
g. Why is water such a good solvent?
Positive ions attract the negative part of
part of water (the oxygen atom),
while negative ions attract the positive part
of water (the Hydrogen atoms).
h. Water’s Temperature-Stabilizing Effects:
What is temperature? Is a way to measure the energy of molecules nonstop vibration
Why is it hard to change the temperature of water?
i. Water’s Cohesion:
What is cohesion? means molecules that resist seperating from one another
How does the cohesion of water molecules help transport water up inside of the tissues of plants? Cohesion makes it possible for columns of liquid water to rise from the roots to the leaves inside narrow pipelines of vascular tissues.
11. Dissolved ions inside of our bodies influence its structure and function. One of the body’s most chemically active ion is the hydrogen ion (H+1).
A.Acids are substances that release or donate hydrogen ions (H+1) to a water (aqueous) solution. Remember that a hydrogen ion is the same thing as a proton since it is a hydrogen atom that has lost its electron.
1. Strong acids ionize completely releasing their hydrogen ions easily. One example is Hydrochloric acid (HCl) found in the stomach.
2. Weak acids may have hydrogen ions to release to solution, but are reluctant or resistant to do so. One example is Carbonic acid (H2CO3) found in soft drinks that is formed when carbon dioxide reacts with water.
B. Bases are substances that accept or bond with hydrogen ions when dissolved in water solutions, thereby removing them or decreasing the number of hydrogen ions remaining in solution. They may also release hydroxide ions (OH-1) to a solution that will then combine with hydrogen ions to form water. These solutions are also known as alkaline solutions. This is how Alka Seltzer got its name. It reduces the acidity of the stomach when someone has acid indigestion.
C. The PH SCALE is used by scientists to represent the nature of a solution relative to the amount of hydrogen ions in solution. The scale extends from a numerical value of 0 to 14 .
1. Solutions with a value of “0” are very Acidic_, meaning there is a high concentration of hydrogen ions in solution.
2. Solutions with a value of “14” are very Basic (alkaline),
meaning there is a very low concentration of hydrogen ions in solution.
3. Pure water has a value of “ 7”, which indicates it is a neutral solution, or in other words one with the same amount of H+1 and OH-1 ions.
4. The pH scale is a type of metric scale. This means that for every change in the pH, there is a ten-fold change in the concentration of hydrogen ions. On the metric scale, to change from one unit of measurement to another it is necessary to move the decimal point either to the right or to the left. Each time the decimal point is moved it is equal to multiplying or dividing by 10. If the decimal moves 3 places to the right it is equal to multiplying the value by 10 X 10 X 10 or the final answer is 1,000 times larger. The following are several examples:
A solution with a pH = 2 is 10 times more acidic than a solution of pH = 3.
A solution with a pH = 5 is 100 times less acidic than a solution of pH = 3.
A solution with a pH = 10 is 100 times more basic than a solution of pH = 8.
A solution with a pH = 6 is 1000 times less basic than a solution of pH = 9.
D. _ are substances that when dissolved in water release ions other than the hydrogen ion (H+1) or hydroxide ion (OH-1). Examples include sodium chloride or table salt (NaCl) and calcium phosphate [ Ca3(PO4)2 ] found in bones. Most salts serve key functions in cells. The ions released into solution in the body are also called “electrolytes”, in that they allow the solution to be able to conduct an electric current.
E. _ are substances that resist a change in pH when an acid or base is added to the solution. They are generally formed by mixing a weak acid and weak base. If a strong acid is added to the mixture, the weak base bonds to the hydrogen ions to neutralize the acid; if a strong base is added to the mixture, the weak acid releases hydrogen ions to neutralize the base. In either case, the pH does not change significantly.
Buffers can only work for so long, then the pH will shift rapidly.
12. Give the approximate pH of each of the following solutions then identify each as an acid (A) [pH of 1-6], base (B) [ph of 8-14] or essentially neutral (N) [pH of 6-8].
1. Tomato juice _ 4, A
2. Human blood _ 8, N
3. Vinegar _ 2, A
4. Pure water _ 7, N
5. Coffee _ 5, A
6. Ammonia _ 11, B
7. Seawater _ 8, N
8. Typical rainwater _ 5, A
9. Oven / Drain cleaner _ 14, B
10. Antacid pills (Tums) _ 9, B
11. Urine _ 5, A
12. Gastric juice _ 1, A
13. Complete the following matching
Chapter review: Answer the following essay questions.
14. a. If a sulfur atom has six electrons in its outer shell of electrons, how many covalent bonds is it likely to form with other atoms? Why?
Two because there are two unpaired electrons.
b. If a hydrogen atom has one electron in its outer shellof electrons, how many covalent bonds is it likely to form with other atoms? Why?
Only one because only one electron is available for pairing.
c. What do you think the chemical formula for hydrogen sulfide would be?
Hint: Look at the location of sulfur compared to oxygen on the periodic table.
H2S because the chemical formula for hydrogen is "H2" and the formula for sulfide is "S."
15. In your own words, explain the main difference between a polar covalent bond and a nonpolar covalent bond.
In nonpolar covalent bonds the atoms have the same electronegativity. This means the atoms equally share electrons. In polar covalent bonds, one atom has more pull than the other.
16. If a water molecule is neutral (has no net charge), then why does it attract polar molecules and repel nonpolar ones.
In each molecule of water, polar covalent bonds join one oxygen atom with two hydrogen atoms. Overall, the molecule has no charge, but the oxygen pulls the shared electrons a bit more than the hydrogen atoms do. Thus, each of the atoms in a water molecule carries a slight charge: The oxygen atom is slightly negative and the hydrogen atoms are slightly positive. This separation of charge means a water molecule is polar.
17. Explain why sweating helps cool the body when it is overheated?
It takes heat to convert liquid water to a gas, so the surface temperature of water decreases during evaporation. Evaporative water loss can help you and some other mammals cool off when you sweat in hot, dry weather. Sweat, which is about 99% water, cools the skin as it evaporates.
Sample Test Questions for chapter 2 and Lab #6:
1. A substance that cannot be broken down into simpler substances by ordinary
chemical means is known as a(n) C
a. molecule
b. ion
c. element
d. compound
e. isotope
2. A sulfur atom has 6 electrons in its outer energy shell. As a result, it tends to form
covalent bonds with other atoms. A
a. 2
b. 3
c. 4
d. 6
e. 8
3. A phosphorus atom has an atomic mass (mass number) of 31 and an atomic number
of 15. How many PROTONS are there in a neutral phosphorus atom? A
a. 15
b. 16
c. 31
d. 46
e. none of the above
4. A is a subatomic particle that carries a charge. B
a. proton……negative
b. electron…..negative
c. neutron…..negative
d. proton…..neutral
e. electron……neutral
5. Isotopes of an element differ in their number of: D
a. electrons
b. bonds formed by the atom
c. protons
d. neutrons
e. nuclei
6. When hydrogen atoms lose one electon to become an ion, their net electrical charge is A
a. +1
b. -1
c. remains neutral
d. impossible to know from just this information provided
BIOL 160: Module 1 - 28 -
7. A solution at pH of 4 contains the concentration of Hydrogen ions A
as the same amount of a solution with a pH of 2.
a. 2 times more
b. 2 times less
c. 20 times more
d. 20 times less
e. 100 times less
8. This property of water makes it possible for columns of liquid water to rise from roots to leaves inside narrow pipelines of vascular tissues inside a plant. A
a. cohesion
b. temperature
c. water sickness
d. surface tension
e. none of the above
9. Bonds that form when atoms transfer one or more electrons are called bonds. A
a. ionic
b. polar covalent
c. hydrogen
d. non-polar covalent
10. Within water molecules, the hydrogen atoms are bonded to the oxygen atom by
bonds, whereas the hydrogen atoms form ___ bonds with
neighboring water molecules.
a. hydrogen…..ionic
b. ionic……hydrogen
c. polar covalent…….ionic
d. polar covalent……hydrogen
e. hydrogen…….polar covalent
11. A solvent is E
a. the dissolving agent of a solution
b. generally the liquid portion of a solution
c. usually water in living organisms
d. generally the portion of a solution found in smaller amount
e. A, B and C are all correct
12. If a sample has a mass of 0.08 grams, what is this mass measured in milligrams?
a. 0.00008
b. 0.008
c. 0.08
d. 8.0
e. 80